Partial Discharge Information 1
Partial Discharge Information 1
Partial Discharge Information 1
Introduction
Partial Discharge testing is a predictive maintenance tool for motor and generator stator windings. It is the only on-line electrical test that correctly identifies and warns of pending stator winding failure mechanisms such as loose windings, contamination, thermal deterioration, poor manufacture, problems due to load cycling and more! The test can be applied to any stator winding 3kV to 26kV. Industry statistics by IEEE and EPRI (Electrical Power Research Institute) indicate that approximately 40% of all machine failures occur due to failure of the stator winding insulation. (See pie chart to right)
Studies show that most stator windings are very reliable (about 95%) at any given time. Knowing this, it is important for users of large machines to know or at least have an idea if they are one of the 5% or not. There are advantages to knowing that there are no problems. Some machines are known to be more reliable than others because of their design and how they are operated. However, eventually these machines will fail, if for no other reason, due to gradual thermal aging of the stator winding insulation. Users of the partial discharge test will be able to find problems while on line and also identify machines that are in good condition enabling them to extend the time between major outages. On-line Partial Discharge testing is the only electrical test that allows you to do this.
3. Purchase a Continuous On-Line Monitor (BusTrac or PDTrac ) to operate in either stand alone mode with alarm or analog outputs, remote control mode or automated mode; 4. Testing Services Have Iris come to site and perform periodic routine testing In any of the above cases, permanently installed PD sensors, 80pF capacitive Bus Couplers (shown to the left) specifically designed to work with partial discharge frequencies (50MHz-250MHz typically) need to be installed. These high voltage capacitors create a high pass filter to allow PD signals through for measurement. Iris has sold over 25,000 of these sensors around the world. Worthy of mention is that not one has ever failed. In fact, the IEEE has specified a theoretical operating life of about 60,000 years!!! Well all be retired by then With only 2 days worth of training, clients can become their own expert on partial discharge testing and interpretation. It's that easy. The reason is simple. Iriss patented noise separation techniques that are built into the system (sensor installation and instrument) objectively separate signals based on where they originate. Thus eliminating false indications. Heres how Iris system works:
2 - 1 Westside Drive, Toronto, Ontario, Canada M9C 1B2 Phone: (416) 620-5600 Fax. (416) 620-1995 www.irispower.com email: sales@irispower.com
Jan 2004
In cases where the machine is connected to the system (breaker, switchgear, etc.) using power cable, AND there is at least 100 feet (straight run, no taps) of power cable between the machine terminals and connected system, one bus coupler per phase can be used. This type of installation is very typical for motors, but on occasion is applied on generators. The reason for only needing one bus coupler is that any High Frequency (HF) electrical noise signals traveling from the system will be significantly attenuated by the >100 of power cable. Since Iris bus couplers operate at HF (>40MHz), noise signals dont pass through the bus couplers. If they were to operate at lower frequencies, more electrical noise would enter the system and make it difficult to separate the PD from electrical noise. Thus, PD testing at high frequencies provides a high Signal-To-Noise Ratio (SNR).
Iris Recommends
As a basis for new clients, Iris recommends PD testing every 6 months for the first 2 years. This will provide a good solid baseline trend for future comparison. From there, depending on the levels of Partial Discharge and how it is changing, Iris recommends, as a minimum, testing no less than once per year. Alternatively, some clients opt to purchase a continuous on-line monitor to continually track and trend the PD activity. This eliminates the need for on-site visits. Our Trac instruments PDTrac and BusTrac will provide maximum warning of increasing PD activity in order for maintenance personnel to act accordingly. They come equipped with alarm relays and optional analog (4-20mA) signal outputs for connection to a DCS or SCADA. Users can also remotely communicate with the Trac monitors via Ethernet, RS485, fibre-optic or wireless. PDTrac also comes equipped with analog input modules to allow condition based triggering on stator winding temp, ambient temp, or humidity. The PDTrac is used with a 3-coupler installation and the BusTrac is used with a 6c-oupler installation. The Trac instruments make life that much easier knowing that PD measurements are always being collected.